UWB Microwave Imaging System with A Novel Calibration Approach For Breast Cancer Detection

ABSTRACT

An apparatus and method for imaging a tissue. The method includes transmitting a first microwave frequency signal to and receiving a first total signal from the tissue at a first position. A second microwave frequency signal is transmitted to and a second total signal received from the tissue at a second position. The first total signal is calibrated with respect to the second total signal and an image is constructed from the calibrated signal.

This application is a continuation of International PCT Application No.PCT/US2011/054952, filed Oct. 5, 2011, entitled “UWB MICROWAVE IMAGINGSYSTEM WITH A NOVEL CALIBRATION APPROACH FOR BREAST CANCER DETECTION”,which claims the benefit of U.S. Provisional Application No. 61/389,863,filed Oct. 5, 2010, entitled “UWB MICROWAVE IMAGING SYSTEM WITH A NOVELCALIBRATION APPROACH FOR BREAST CANCER DETECTION”, the disclosures ofwhich applications are hereby incorporated by reference herein in theirentireties.

FIELD OF THE INVENTION

The present invention relates generally to medical imaging modalitiesand, more particularly, to a microwave imaging system.

BACKGROUND OF INVENTION

Microwave imaging technology is attractive as an alternative solutionfor tumor detection, and particularly, for breast cancer detection.Microwave imaging technology is lower-cost and shorter operation time ascompared to magnetic resonance imaging (“MRI”) and is less invasive thanX-ray.

However, a problem associated with microwave imaging is the low contrastcondition for the detection of a malignant tumor. Recent studies haveindicated that nearly all breast cancers originate in the glandulartissues of the breast. The dielectric property differences betweenmalignant tissues and glandular tissue is generally not more than 10%.With this slight difference in dielectric properties, the expectedreflected/scattered signal from the malignant tumor is very weak. Onethe other hand, the received signals due to skin backscatter andcoupling of the transmitting and receiving antenna (“Tx” and “Rx,”respectively) are comparatively much stronger. Therefore, the desiredsignal from the tumor is typically immersed in various noise signals.

Conventional methods for overcoming the desired signal to noise ratiohave included various calibration and contrast agents. In calibratingthe signal, generally the signal acquired from a known, non-tumor regionof the breast tissue is subtracted from the signal acquired from thetumor containing region. While this method has been useful ineliminating noise, the method is not practical for real clinicaldiagnosis since the reference signal is not generally available.Contrast agents, such as golden nano-particles or carbon nano-tubes havebeen considered; however, some patients may not accept any agentinjections.

Therefore, there continues to be a need for signal processing methodsthat improve the sensitivity of tumor detection by microwave imagingtechnologies.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and othershortcomings, drawbacks, and challenges of the conventional microwaveimaging technology by presenting a diagnostic imaging device and methodthat uses microwave imaging for identify a target, such as a tissue massor tumor, by calibrating an acquired microwave signal prior to imageconstruction. While the invention will be described in connection withcertain embodiments, it will be understood that the invention is notlimited to these embodiments. To the contrary, this invention includesall alternatives, modifications, and equivalents as may be includedwithin the spirit and scope of the present invention.

In accordance with one embodiment of the present invention, a method forimaging a tissue includes transmitting a first microwave frequencysignal to and receiving a first total signal from the tissue at a firstposition. A second microwave frequency signal is transmitted to and asecond total signal received from the tissue at a second position. Thefirst total signal is calibrated with respect to the second total signaland an image is constructed from the calibrated signal.

According to another embodiment of the present invention, a medicalimaging device includes a tissue support having a size and shape toreceive a tissue. At least one transducer is operably coupled to thetissue support. The at least one transducer includes a transmittingantenna operable in a frequency range of about 2 GHz to about 8 GHz anda receiving antenna operable in a frequency range of about 2 GHz toabout 8 GHz. The at least one transducer transmits a first signal andreceives a first total signal at a first position with respect to thetissue and transmits a second signal and receives a second total signalat a second position with respect to the tissue.

Still, in accordance with another embodiment of the present invention, amedical imaging device includes a tissue support having a size and shapeto receive a tissue. A plurality of transducers is coupled to the tissuesupport. Each of the plurality of transducers includes a transmittingantenna operable in a frequency range of about 2 GHz to about 8 GHz anda receiving antenna operable in a frequency range of about 2 GHz toabout 8 GHz. A select one of the plurality of transducers transmits afirst signal and receives a first total signal at a first position andan adjacent one of the plurality of transducers transmits a secondsignal and receives a second total signal at a second position.

One embodiment of the present invention is directed to a method ofreconstructing an imaging of a tissue from first and second microwavesignals and includes receiving the first and second microwave signals asreflected from the tissue at respective first and second positions. Thefirst microwave signal is calibrated with the second microwave signaland the image is constructed form the calibrated signal.

Another embodiment of the present invention is directed to a method ofscanning a tissue and includes transmitting a first microwave frequencysignal to the tissue at a first position. A first total signal reflectedfrom the tissue at the first is received. A second microwave frequencysignal is transmitted to the tissue at a second position, and a secondtotal signal reflected from the tissue at the first is received. Thefirst and second positions are separated by less than about 20 mm.

The above and other objects and advantages of the present inventionshall be made apparent from the accompanying drawings and thedescriptions thereof.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention.

FIG. 1 is a perspective view of a microwave imaging system having twoimaging cups for detection of breast cancer in accordance with oneembodiment of the present invention.

FIG. 2 is a side elevational view of an imaging transducer in accordancewith one embodiment of the invention.

FIG. 3 is a flow chart illustrating one method of transmitting andacquiring a microwave signal in accordance with one embodiment of theinvention.

FIG. 4 is a schematic electrical diagram of the imaging system inaccordance with one embodiment of the present invention.

FIG. 5 is a diagrammatic view of a computer system suitable for use withthe microwave imaging system in accordance with one embodiment of thepresent invention.

FIG. 6 is a flow chart illustrating one method of processing theacquired signal in accordance with one embodiment of the presentinvention.

FIG. 7 is a graphical illustration of the acquired signals from twoadjacent positions.

FIG. 8 is a graphical illustration of the processed signal from the twoacquired signal of FIG. 7.

FIG. 9 is an exemplary image reconstructed from acquired signals inaccordance with an embodiment of the present invention.

FIG. 10 is an imaging cup in accordance with another embodiment of thepresent invention.

FIG. 11 is an imaging cup in accordance with still another embodiment ofthe present invention.

FIG. 12 is perspective view of a microwave imaging system incorporatedinto a brassiere for detection of breast cancer in accordance withanother embodiment of the present invention.

FIG. 13 is a cross-sectional view of the brassiere of FIG. 12, takenalong the line 13-13 in FIG. 12.

FIG. 14 is a perspective view of a microwave imaging system incorporatedinto a brassiere for detection of breast cancer in accordance with stillanother embodiment of the present invention.

FIG. 15 is a perspective view of a microwave imaging system incorporatedinto a brassiere for detection of breast cancer in accordance withanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures, an imaging system in accordance with variousembodiments of the present invention is described. The imaging systemmay include a tissue cup, for example, an imaging cup, in the shape ofthe tissue being imaged. The imaging cup, such as for use in imagingbreast tissue, may be rigid, may include a disposable polymeric hygienicliner, and may include at least one microwave antenna. The liner may bepolyurethane or silicone gel, such as those that arecommercially-available from Ohio Willow Wood (Mt. Sterling, Ohio). Theliner increases patient comfort, reduces air bubbles at the skininterface, minimizes skin slippage, and may decrease the dielectricimpedance mismatch for optimal signal propagation. It is readilyunderstood by those skill in the art that additional electronics areincorporated via wire or traces to access, drive, and/or process themicrowave antenna and the signals transmitted and/or received by thesame.

The sending and receiving of microwave signals may be achieved byvarious types and designs of antennae, the size of which is largelygoverned by the dielectric constant, ε_(r), of the fabricationmaterials. One such example is a patch antenna. Dielectric resonators orany other microwave device may also be used for signal transmission andreception. These microwave antennae or resonators may be positioned, orarrayed, within the imaging cup. Various sizes of imaging cups may berequired for appropriately fitting the particular anatomy of the patientto ensure skin contact with the antennae or resonators. Thus, the numberof antennae or microwave devices required is related to the surfacedensity, wherein a larger number of antennae is required for a breasthaving a larger surface area. The rigidity of the cup reduces, oreliminates, movement between the individual microwave devices.

Some embodiments may include a cup assembly that seals the antenna(e)into a conformable polymeric material. The polymeric material may be thesame described above and may be used with a hygienic liner. Thepolymeric material may reduce or eliminate the need for gels or otherimpedance matching material.

With reference now in particular to FIG. 1, a microwave imaging system(“imaging system” 10) for use in detecting breast cancer in accordancewith one embodiment of the present invention is described. The imagingsystem 10 includes a planar support 12 with first and second tissuesupports 14, 16 therein, wherein the tissue supports are specificallyillustrated as breast imaging cups. The imaging system 10 may bearranged such that the patient (not shown) may lie upon the planarsupport 12 with the left breast (not shown) in a first imaging cup 14and the right breast (not shown) in the second imaging cup 16.

It will be readily appreciated that while the features of the presentinvention are described with reference to breast imaging, the variousfeatures may be altered, as would be known to those of ordinary skill inthe art, for imaging other portions of a patient's anatomy. Furthermore,while the planar support 12 is schematically illustrated as a basicsupport, it would be readily understood that the first and secondimaging cups 14, 16 may alternatively be positioned in an examinationtable or a rotatable table that may be rotated to an upright position sothat the patient, with the table, may together be rotated into thesupine position.

In still other embodiments, the first and second imaging cups 14, 16 maybe formed separate from any planar support and positioned directly ontothe breasts. Moreover, only one imaging cup may be used, with one breastimaged first and then the other breast imaged subsequently. Moreover,and as described in greater detail below, the imaging cups may also beformed separately and incorporated into a supportive brassiere 17 forthe patient to wear during imaging, allowing a more comfortable stancefor the patient.

In the particular illustrated embodiment, the first and second imagingcups 14, 16 may have a shape that is conical, hemispherical,paraboloidal, or other as appropriate to receive the patient's breast.

Each imaging cup 14, 16 includes a plurality of transducers 18, 20, eachtransducer 18, 20 being located at a position, P^(i), along the surfaceof the imaging cup 14, 16. Any number of transducers 18, 20 may be usedand may be arranged, as shown, in one or more rows with each adjacenttransducer being separated by a small distance (in Cartesiancoordinates) or small angle (in polar coordinates), for example, about 1degree, about the circumference of the imaging cup 14, 16. As describedin greater detail below, other arrangements may also be used, and thearrangements of the imaging cups should not limited to the particularshape and number of transducers shown.

Turning now to FIG. 2, one transducer is shown in greater detail. Thetransducer 18, 20 includes transmitting and receiving antenna 22, 24(“Tx” and “Rx,” respectively) for transmitting a first electromagneticsignal and receiving a second electromagnetic signal in accordance withthe general concepts of microwave imaging technologies. As is well knownby those of ordinary skill in the art, a single antenna may also act asa whole, and may be used for both the transmitting and receivingfunctions, alternatively eliminating the need for the separate Tx and Rxantennae 22, 24. The single antenna may also be used for Tx and Rx at asingle point in time and switched to the opposite mode when needed. TheTx and Rx antennae 22, 24 may be fabricated on a substrate 26, which,for example, may include a 31-mil thick Rogers RT5880 substrate (RogersCorp. Rogers, Conn.) having a dielectric constant, k, of about 2.2 and aloss tangent of about 0.0009. An adaptor 28 may be configured toelectrically-couple the transducer 18, 20 to the various otherelectrical components of the imaging system 10 (FIG. 1). In would bereadily appreciated that other fabrication tools and methods may also beused, as is known to those of ordinary skill in the art.

Generally, the Tx antenna 22 transmits the electromagnetic signal,operating, for example, in the frequency range of about 2 GHz to about 8GHz. The transmitted first signal is scattered and/or reflected atvarious interfaces of varying dielectric characteristics, which mayinclude the tissue-air interface and the interface between the glandulartissue of the breast and the malignant tumor tissue, e.g., a target,therein. The Rx antenna 24 receives the various reflected and/orscattered second signals, which may include signals as a result ofsignal coupling of the Tx and Rx antennae 22, 24, backscatter from thetissue-air interface, reflections from the target, miscellaneousreflections, and other signals as are known to those of ordinary skillin the art. The Rx antenna 24 operates, for example, in the frequencyrange of about 2 GHz to about 8 GHz.

With reference to FIGS. 3 and 4, as well as continued reference to FIG.2, the electronic arrangement and a method 30 of generating thetransmitted signal, transmitting the signal, receiving thescattered/reflected signal, and preparing the received signal are shownand described in greater detail.

Operation of the transducer 18, 20 begins with generating a signal(Block 32) at an alternating signal generator 34. More specifically,signal generation may include a driving clock that is used to drive apulse generator. In some embodiments, an FPGA circuit may be used togenerate the driving clock, which drives a 300 ps Gaussian pulsegenerator. The alternating signal may then be mixed with an oscillatingsignal 36, such as input from a voltage control oscillator 38, andamplified (Block 40). Mixing of the signal may occur in a signal mixer42, such as a MITEQ DM0208 mixer (MITEQ Inc., Hauppauge, N.Y.), andamplified by a high-gain amplifier 44, such as a Mini-Circuits ZVE-8G+Power Amplifier (Mini-Circuits, Brooklyn, N.Y.). The amplified signal isthen transmitted to a wideband transmitter link of the transducer 18, 20and transmitted by the Tx antenna 22 (Block 46). The Tx antenna 22operates at 2-8 GHz to balance the competing requirements for imagingresolution and penetration depth into the breast tissue.

The signal is received by the Rx antenna 24 of the transducer 18, 20(Block 48) and amplified, divided, and mixed (Block 50). In that regard,the received signal is amplified through a wideband low noise amplifier52, such as the commercially-available Hittite HMC753 (Hittite MicrowaveCorp., Chelmsford, Mass.) and down-converted into an in-phase channel(illustrated as “I”) and a quadrature-phase channel (illustrated as“Q”). The I and Q channel signals I, Q are each mixed at first andsecond mixers 58, 60, respectively, with the oscillating signal 36 thatwas generated by the voltage control oscillator 38. Each signal may thenbe low-pass filtered and converted at a respective analog-to-digitalconverter (“ADC” 62, 64). One suitable ADC 62, 64 may include thecommercially-available MAX104 (Maxim Integrated Products, Inc.,Sunnyvale, Calif.). Once converted to digital form, all collectedsignals may be stored, for example, in a field-programmable gate array(“FPGA”), such as the commercially-available Xilinx Vertex-4 FPGAevaluation board (Xilinx, Inc., San Jose, Calif.). Alternatively, oradditionally, the signals may be transferred to a computer 66, such asby a USB2.0 (not shown) or wirelessly-transmitted using BLUETOOTH(Bluetooth Special Interest Group, Kirkland, Wash.) or any other robustdata transfer protocol as is well known in the art, where the signal maybe reconstructed (Block 68).

With reference to FIG. 5, the details of the computer 66 for operatingthe transducers 18, 20 (FIG. 2) and/or reconstructing the images fromthe acquired microwave signals is described. The computer 66 that isshown in FIG. 5 may be considered to represent any type of computer,computer system, computing system, server, disk array, or programmabledevice such as multi-user computers, single-user computers, handhelddevices, networked devices, or embedded devices, etc. The computer 66may be implemented with one or more networked computers 70 using one ormore networks 72, e.g., in a cluster or other distributed computingsystem through a network interface (illustrated as “NETWORK I/F” 74).The computer 66 will be referred to as “computer” for brevity's sake,although it should be appreciated that the term “computing system” mayalso include other suitable programmable electronic devices consistentwith embodiments of the present invention.

The computer 66 typically includes at least one processing unit(illustrated as “CPU” 76) coupled to a memory 78 along with severaldifferent types of peripheral devices, e.g., a mass storage device 80with one or more databases (not shown), an input/output interface(illustrated as “USER I/F” 82), and the Network I/F 74. The memory 78may include dynamic random access memory (“DRAM”), static random accessmemory (SRAM”), non-volatile random access memory (“NVRAM”), persistentmemory, flash memory, at least one hard disk drive, and/or anotherdigital storage medium. The mass storage device 80 typically includes atleast one hard disk drive, and may be located externally to the computer66, such as in a separate enclosure or in one or more of the networkedcomputers 70, one or more networked storage devices 84 (including, forexample, a tape or optical drive), and/or one or more other networkeddevices (including, for example, a server).

The CPU 76 may be, in various embodiments, a single-thread,multi-threaded, multi-core, and/or multi-element processing unit (notshown) as is well known in the art. In alternative embodiments, thecomputer 66 may include a plurality of processing units that may includesingle-thread processing units, multi-threaded processing units,multi-core processing units, multi-element processing units, and/orcombinations thereof as is well known in the art. Similarly, the memory78 may include one or more levels of data, instruction, and/orcombination caches, with caches serving the individual processing unitor multiple processing units (not shown) as is well known in the art.

The memory 78 of the computer 66 may include one or more applications(illustrated as “PROGRAM CODE” 88), or other software program, which areconfigured to execute in combination with an operating system(illustrated as “OS” 86) and automatically perform tasks necessary foroperating the transducers 18, 20 (FIG. 2) and/or reconstructing theimages with or without accessing further information or data from thedatabase(s) of the mass storage device 80.

Those skilled in the art will recognize that the environment illustratedin FIG. 5 is not intended to limit the present invention. Indeed, thoseskilled in the art will recognize that other alternative hardware and/orsoftware environments may be used without departing from the scope ofthe invention.

In use, and with reference now to FIG. 6, a method 90 of reconstructingan image from the acquired signals is described. A first transducer 18,20 (FIG. 1) associated with either or both of the first and secondimaging cups 14, 16 (FIG. 1) and located at a first position, P_(i), isoperated and a signal received, S^(i)(t) (Block 92), wherein the totalsignal is given by:

S _(i)(t)=S _(coupling) ^(i)(t)+S_(skin) ^(i)(t)+S _(target) ^(i)(t)+S_(mr) ^(i)(t)

where S_(coupling) ^((t)) is the portion of the signal due to the mutualcoupling between the Tx antenna and the Rx antenna, S_(skin) ^((t)) isthe portion of the signal due to backscatter at the air/skin interface,S_(target) ^((t)) is the portion of the signal due to thereflection/scattering from the target, i.e., the tumor, and S_(mr)^((t)) is the portion of the signal due to multi-reflections.

Sequentially, or simultaneously, a transducer 18, 20 (FIG. 1) associatedwith either or both of the first and second imaging cups 14, 16 (FIG. 1)and located at a second position, P_(i+1), is operated and a signalreceived, S^(i+1)(t), (Block 94) wherein the total signal is given by:

S ^(i+1)(t)=S _(coupling) ^(i+1)(t)+S _(skin) ^(i+1)(t)+S _(target)^(i+1)(t)+S _(mr) ^(i+1)(t)

After the signal at the second position is acquired, a determination ismade as to whether “n” signals have been acquired (Block 96). That is,if the first imaging cup 14 (FIG. 1) includes 50 transducers 18 (FIG.1), then signals from each of the 50 transducers 18 (FIG. 1) should beacquired and n would equal 50. Alternatively, if a single transducer 98(FIG. 11) is used, such as is illustrated and described below withreference to FIG. 11, then a discrete number of positions of the singletransducer 98 (FIG. 11) along the track 100 should be acquired. Forexample, if the position of the single transducer 98 (FIG. 11) is moveby 1 degree for each position, then n would equal 360.

If n signals have not been acquired (“NO” branch of Decision Block 96),then the method 90 returns to further acquire a signal at anotherposition (Block 94). Otherwise, the process continues.

Examples of S^(i)(t) and S^(i+1)(t) acquired at P_(i) and P_(i) areshown in FIG. 7. The signals at the first and second positions includeat least three regions of interest, including: (A) combination ofS_(coupling) ^(i)(t) and S_(skin) ^(i)(t); (B) S_(target) ^(i)(t), whichis immersed within the noise and other scattered signals; and (C) S_(mr)^(i)(t). The signal attributed to reflection at the tumor/glandulartissue interface has an intensity that is substantially equal to thenoise signals within the same region of interest. Thus, isolation ofS_(target) ^(i) within the total acquired signal is difficult.

To extract the target signal, S_(target) ^(i)(t) in accordance with oneembodiment of the present invention, the signals measured from the firstand second positions, S^(i)(t), S^(i+1)(t), are then calibrated. As anavailable choice, the frequency response of the coupling between the Txand Rx antennae 22, 24 may also be measured in an antenna chamber (notshown) and used to separate the skin reflections, S_(skin) ^(i)(t). Inthat regard, a tissue boundary in each acquired signal is determined(Block 102).

In some embodiments, such as is shown in FIG. 13, a polymeric liner 103may be used to match the impedance with the breast 105 and to eliminateair at the skin boundary of the breast 105 for optimal signalpropagation across the skin boundary. The polymeric liner 103 alsosimplifies computational modeling of the received signals. The polymericliner 103 may be flexible and constructed from a polymer material havingsuitable dielectric properties for transmission of the microwavesignals. The polymer material may be disposable, such as after a singleuse/patient. In still other embodiments, such as is shown in FIG. 13,the transducers 106 may be encapsulated within the polymer materialcomprising the polymeric liner, and wherein an additional liner 108 maybe used for hygienic purposes. The additional liner 108 may also includethe fabric of the brassiere 17 (FIG. 12), which may, itself, be washableor disposable. Use of the polymeric liner 103 may reduce and/oreliminate the need for matching gels; however, use of such matching gelsis not precluded. Furthermore, though not specifically shown, thepolymeric liner 103 may be incorporated into other embodiments of thepresent invention, including, for example, the imaging cups 14, 16 ofFIG. 1.

With the tissue boundary identified, the signal acquired at eachposition is corrected with the signal acquired at an adjacent position.More specifically, the signal acquired at the first position, P_(i), iscorrected by subtracting the signal acquired at the second position,P_(i+1) (Block 104). The corrected signal, S_(corrected)(t), isgenerally described as a mid-point between the first and secondpositions and is given by:

S _(corrected)(t)=S ^(i+1)(t)−S ^(i)(t)

One example of a corrected signal shown in FIG. 8. Since the positionsof Tx and Rx antennae 22, 24 (FIG. 2) are fixed, the signal due tocoupling, S_(coupling) ^(i)(t), is constant and cancelled in thecalibration process. The signal due to backscatter from the skininterface, S_(skin) ^(i)(t), are largely eliminated via calibration aswell. Finally, signals due to multi-reflections, S_(mr) ^(i)(t), have alonger time delay and may be gated in the time domain.

With S_(corrected)(t) calculated, the signal due to the target,S_(target) ^(i)(t), is readily identifiable as compared with thesurrounding noise. Said another way, the signal-to-noise ratio betweenthe signal due to the target, S_(target) ^(i)(t), is significantlygreater in S_(corrected)(t) as compared to S^(i)(t) or S^(i+1)(t).

Returning again to FIG. 6, with the corrected signal calculated, animage may be reconstructed from the each S_(corrected) ^((i+1)−i) (Block106). While image reconstruction may include various algorithms andcomputational methods, one suitable image reconstruction may be, forexample, a three-dimensional beamformer used to recover the targetimage. More specifically, one suitable beamformer is provided in detailin Y. WANG et al. “Three-Dimensional Through Wall Imaging Using an UWBSAR,” IEEE AP-S Int. Symp. On Anteannas and Propagat. Toronto, Calif.(July 2010). Briefly, the imaged breast may be divided into cubic voxelsin x-, y-, and z-planes. For a given voxel, V(x, y, z), a delay and sum(“DAS”) algorithm is applied to calculate image information. The DASalgorithm is given by:

${S\left( {x,y,z} \right)} = {\sum\limits_{m = 1}^{M}{\sum\limits_{n = 1}^{N}{{w_{m,n}\left( {x,y,z} \right)}s_{m,n}^{j\; {\phi_{m,n}{({x,y,z})}}}}}}$

Where is the signal received by the Rx antenna at P_(i) (“m”) andP_(i+1) (“n”),_(n w) _(m,n)(x, y, z) introduces the magnitudecompensation for different scattering loss and propagation loss, andφ_(m,n)(x, y, z) introduces the phase compensation for different phasedelays. The DAS algorithm is applied to each S_(corrected) ^((i+1)−i)(t)and the completed three-dimensional image is displayed, one example ofwhich is shown in FIG. 9.

Referring specifically to the reconstructed image of FIG. 9, the regionindicated by the high intensity, normalized signal, e.g., S_(target)^(i)(t) is associated with the target or tumor.

Turning now to FIGS. 10 and 11, imaging cups 120, 122 in accordance withadditional embodiments of the present invention are shown and described.In particular, in FIG. 10, the transducers 124 are positionedcircumferentially about the imaging cup along a single plane 126 throughthe imaging cup 120. The transducers 124 may be arranged in any type ofconfiguration around the imaging cup 120. The particular embodiment ofthe imaging cup 120 reduces the number of signals “n,” to be acquiredand the number of corrected signals, S_(target) ^(i)(t), to becalculated, thus reducing manufacturing costs, image construction time,and computer hardware and software capabilities.

In FIG. 11, still another imaging cup 122 and comprises the singletransducer 98 and the track 100. A motor (not shown) is configured tomove the transducer 98, by a discrete distance, along the track 100 foracquiring the signals, S^(i+1)(t), from the “n” positions. While theparticular embodiment includes only one transducer 98 and significantlyreduces the amount of antenna-coupling from adjacent transducers 18(FIG. 1), movement of the individual transducer 98 along the track 100may increase the procedure time required for imaging one breast. Instill other embodiments, multiple transducers may be operably coupled tothe track 100, or alternatively, associated with separate tracks withinthe imaging cup.

Turning now to FIG. 12, the brassiere 17 for use with the imaging systemin accordance with one embodiment of the present invention is describedin greater detail. The brassiere may be constructed, as noted above,from a washable or disposable material and includes a chest portion 130,shoulder straps 132, 134, and chest straps 136, 138. The chest portion130 may be sized and shaped with cups for receiving the left and rightbreasts, as indicated above. Accordingly, various brassiere sizes may bemanufactured and correspond to conventional brassiere sizing.

The chest portion 130 may further include one or more coupling devices140 that are configured to operably couple one or two imaging cups 142,144 to the chest portion 130. Each of the imaging cups 142, 144 may beconstructed from material similar to the polymeric liner 103 (FIG. 13)described above, which may include an outer covering material ifdesired. Accordingly, the imaging cups 142, 144 would be coupled to thebrassiere 17 via the one or more coupling devices 140 during the signalacquisition protocol. Yet, it would be readily understood that thepolymeric liner material need not be required.

In FIG. 14, the imaging cups 142, 144 are shown with the plurality oftransducers 106 shown in phantom. As was described above, the pluralityof transducers 106 may be arranged in one or more rows with eachadjacent transducer being separated by a small distance or angle.Alternatively, and as shown in FIG. 15, the brassiere 17 in accordancewith another embodiment is shown wherein the imaging cup 142, 144includes a track 152 that is similar to the track 100 (FIG. 11)described above. The track may be radial, as was shown in FIG. 11, ormay be spiral in shape to cover the entire area of the breast forimaging by a single transducer or a transducer array.

While the present invention has been illustrated by a description ofvarious embodiments, and while these embodiments have been described insome detail, they are not intended to restrict or in any way limit thescope of the appended claims to such detail. Additional advantages andmodifications will readily appear to those skilled in the art. Forexample, it will be appreciated that a tissue support or imaging cup mayhave different geometries depending upon the tissue to be imaged. Thus,while the term “cup” is used herein in connection with imaging breasttissue, it will be appreciated that an imaging cup consistent with theinvention need not necessarily have a cup-like shape. The variousfeatures of the invention may be used alone or in any combinationdepending on the needs and preferences of the user. This has been adescription of the present invention, along with methods of practicingthe present invention as currently known. However, the invention itselfshould only be defined by the appended claims.

What is claimed is:
 1. A method of imaging a tissue, the methodcomprising: transmitting a first microwave frequency signal to thetissue at a first position; receiving a first total signal reflectedfrom the tissue at the first position; transmitting a second microwavefrequency signal to the tissue at a second position; receiving a secondtotal signal reflected from the tissue at the second position;calibrating the first total signal with the respect to the second totalsignal; and constructing an image of the tissue from the calibratedsignal.
 2. The method of claim 1, wherein the second position isradially-spaced away from the first position by an angle that rangesfrom about 0.5 degrees to about 5 degrees.
 3. The method of claim 1,wherein the second position is linearly-spaced away from the firstposition by a distance that ranges from about 1 mm to about 20 mm. 4.The method of claim 1, wherein the tissue comprises a glandular softtissue and includes at least one mass located therein.
 5. The method ofclaim 4, wherein the first and total signals each include a firstportion having reflections due to a tissue-air interface, a secondportion having reflections due to a transmitter-receiver coupling, athird portion having reflections due to the at least one mass, and afourth portion having reflections due to multiple scatterings.
 6. Themethod of claim 1, wherein transmitting each of the first and secondtotal signals further comprises: generating an alternating signal;mixing the alternating signal with an oscillating clock signal;amplifying the mixed signal at a high-gain amplifier; and transmittingthe amplified, mixed signal to a transmitting antenna.
 7. The method ofclaim 1, wherein receiving each of the first and second total signalsfurther comprises: amplifying received first and second total signals ata low-noise amplifier; down-converting the amplified signal into twochannels; mixing the down-converted signal of each of the two channelswith an oscillating clock signal; and converting the mixed signal fromeach of the two channels to a respective digital signal.
 8. The methodof claim 1, wherein calibrating the first total signal includessubtracting the second total signal from the first total signal.
 9. Themethod of claim 1, wherein constructing the image further comprises:applying a delay and sum algorithm to the calibrated first signal. 10.The method of claim 1, wherein a first transducer transmits the firstmicrowave frequency signal and receives the first total signal and asecond transducer transmits the second microwave frequency signal andreceives the second total signal.
 11. The method of claim 1, wherein atransducer transmits the first microwave frequency signal and receivesthe first total signal at the first position and is then moved to thesecond position for transmitting the second microwave frequency signaland receiving the second total signal.
 12. A medical imaging devicecomprising: a tissue support having a size and shape to receive atissue; at least one transducer operably coupled to the tissue support,the at least one transducer having a transmitting antenna and areceiving antenna, the transmitting antenna operable in a frequencyrange of about 2 GHz to about 8 GHz and the receiving antenna operablein a frequency range of about 2 GHz to about 8 GHz; and wherein the atleast one transducer transmits a first signal and receives a first totalsignal at a first position with respect to the tissue and transmits asecond signal and receives a second total signal at a second positionwith respect to the tissue.
 13. The medical imaging device of claim 12,wherein the tissue support is a breast imaging cup.
 14. The medicalimaging device of claim 13, wherein the breast imaging cup is operablycoupled to a brassiere.
 15. The medical imaging device of claim 14further comprising: a track operably coupled to the tissue support, theat least one transducer moveable along the track between the firstposition and the second position.
 16. The medical imaging device ofclaim 12 wherein the transmitting antenna and the receiving antenna arethe same antenna.
 17. A medical imaging device comprising: a tissuesupport having a size and shape to receive a tissue; a plurality oftransducers operably coupled to the tissue support, each of theplurality of transducers having a transmitting antenna and a receivingantenna, the transmitting antenna operable in a frequency range of about2 GHz to about 8 GHz and the receiving antenna operable in a frequencyrange of about 2 GHz to about 8 GHz, wherein a select one of theplurality of transducers transmits a first signal and receives a firsttotal signal and an adjacent one of the plurality of transducerstransmits a second signal and receives a second total signal.
 18. Themedical imaging device of claim 17, wherein each of the plurality oftransducers is radially-spaced away from an adjacent one of theplurality of transducers by an angle that ranges from about 0.5 degreesto about 5 degrees.
 19. The medical imaging device of claim 17, whereineach of the plurality of transducers is linearly-spaced away from anadjacent one of the plurality of transducers by a distance that rangesfrom about 1 mm to about 20 mm.
 20. The medical imaging device of claim17 further comprising: a controller configured to calculate a calibratedsignal by subtracting the second total signal from the first totalsignal.
 21. The medical imaging device of claim 20, wherein thecontroller is further configured to construct an image of the tissuefrom the calibrated signal.
 22. The medical imaging device of claim 17,wherein the tissue support is a breast imaging cup.
 23. The medicalimaging device of claim 22, wherein the breast imaging cup is operablycoupled to a brassiere.
 24. The medical imaging device of claim 17,wherein the medical imaging device is part of an imaging system thatincludes a support configured to support the at least one medicalimaging device in an anatomical arrangement suitable for imaging atissue of a patient.
 25. The medical imaging device of claim 24, whereinthe imaging system further includes: a second tissue support having asize and shape to receive a tissue; a second plurality of transducersoperably coupled to the second tissue support, each of the secondplurality of transducers having a transmitting antenna and a receivingantenna, the transmitting antenna operable in a frequency range of about2 GHz to about 8 GHz and the receiving antenna operable in a frequencyrange of about 2 GHz to about 8 GHz, wherein a select one of the secondplurality of transducers transmits a third signal and receives a thirdtotal signal and an adjacent one of the second plurality of transducerstransmits a fourth signal and receives a fourth total signal, and eachof the tissue supports is a breast imaging cup, one of the tissue cupsbeing configured to receive a left breast and the tissue cup beingconfigured to receive a right breast.
 26. The medical imaging device ofclaim 17 wherein the transmitting antenna and the receiving antenna arethe same antenna.
 27. A method of reconstructing an image a tissue fromfirst and second microwave signals, the method comprising: receiving thefirst microwave signal reflected from the tissue at a first position;receiving the second microwave signal reflected from the tissue at asecond position; calibrating the first microwave signal with the respectto the second microwave signal; and constructing an image of the tissuefrom the calibrated signal.
 28. A method of scanning a tissue, themethod comprising: transmitting a first microwave frequency signal tothe tissue at a first position; receiving a first total signal reflectedfrom the tissue at the first position; transmitting a second microwavefrequency signal to the tissue at a second position; and receiving asecond total signal reflected from the tissue at the second position,wherein, the first and second positions are separated by less than about20 mm.